William O'Brien State Park

William O’Brien State Park sits along the western bank of the St. Croix River about an hour north of the Twin Cities, near the small town of Marine on St. Croix. The park protects about 1,880 acres and draws visitors with a combination of river access, wooded trails, and one of the better-developed campgrounds in the Minnesota state park system. What sets it apart is the ongoing restoration of oak savanna habitat, a rare landscape that once dominated this region and now serves as a living example of ecological recovery.

St. Croix River Access and Canoeing

The St. Croix River is the centerpiece of the park experience. The park’s St. Croix public water access is currently closed through construction completion, though it may reopen as water levels allow; canoes and kayaks can launch on the St. Croix farther down the shoreline. The calm stretches near the park are well suited to beginners and families. Canoe rentals are available through the park during summer months, making it easy to get on the water without your own gear. Lake Alice is currently closed to public water recreation during the reconstruction project; the beach, fishing pier, and accessible canoe/kayak launch are closed through construction completion, currently estimated for fall 2027. Fishing is possible from shore along the St. Croix River, but Lake Alice fishing access is currently closed through construction completion, though fishing is more of an incidental activity here than a primary draw.

Oak Savanna Restoration

One of the more distinctive features of William O’Brien is the active restoration of oak savanna, a fire-adapted landscape that once covered vast portions of the upper Midwest but has been reduced to scattered remnants. Park staff and volunteers have worked to remove invasive shrubs, conduct controlled burns, and reestablish the open, grassy understory that characterizes this habitat. Visitors walking through the restored sections will notice a noticeably different feel compared to the denser woodland elsewhere in the park: widely spaced oaks, open sightlines, and a rich ground layer of native grasses and wildflowers in summer. Interpretive signs along some trails explain the restoration process and the ecological role savanna plays for birds and pollinators.

Hiking the Park Trails

The park has about 16 miles of hiking trails spread across two main units divided by Highway 95. Trails range from easy riverside walks to moderate climbs up the bluffs above the St. Croix, where views of the river valley open up through the trees. The upper unit trails wind through the restored savanna and mixed forest, while the lower unit stays closer to the river and lake. Trails are generally well marked and maintained, though some sections can be muddy in spring or after heavy rain. William O’Brien has 12 miles of groomed cross-country and skate ski trails in winter when snow conditions allow.

Camping

William O’Brien offers more than 120 drive-in campsites along with a smaller number of walk-in sites for those who want a bit more separation from the main camping area. Electrical hookups are available at a portion of the sites. The campground is heavily used on summer weekends, and sites often fill well in advance from late June through August. A group camp area can accommodate larger gatherings. Showers and flush toilets are available in the main campground, and four camper cabins provide an option for those looking for something between tent camping and a full cabin rental. The Lake Alice swim beach is currently closed through construction completion, currently estimated for fall 2027.

Pet Policy

Pets are welcome at William O’Brien but must be kept on a leash no longer than six feet at all times. Leashed pets are allowed on trails and in the campground. Pets are not permitted on the swim beach or in any park buildings. Owners are responsible for cleaning up after their animals throughout the park.

Wildlife to Be Aware Of

White-tailed deer are common throughout the park and are often seen along trails, particularly in the early morning and evening hours. While deer are not aggressive, they can startle hikers at close range, and drivers should be alert on the park road at dawn and dusk.

Ticks are present throughout the grassy and wooded areas of the park from spring through fall. Deer ticks, which can carry Lyme disease, are a genuine concern in this region. Wear long sleeves and pants when hiking, use insect repellent with DEET on exposed skin and clothing, and do a full-body tick check after every outing. Check children and pets carefully as well.

Poison ivy grows widely along trail edges, forest margins, and riparian zones near the river. Learn to identify the three-leaflet pattern before your visit, and stay on established trails to reduce contact. Wash any exposed skin promptly if you suspect contact.

Black bears are uncommon in this part of Minnesota; if one is seen, follow standard bear-safety practices and secure food and scented items. Store all food, coolers, and scented items in your vehicle or a hard-sided container when camping. Never leave food unattended at a campsite.

Practical Information

William O’Brien State Park is located at 16821 O’Brien Trail North, Marine on St. Croix, Minnesota 55047. From the Twin Cities, take Interstate 35E or 35W north to Highway 8 east, then travel north on Highway 95 to the park entrance. The nearest town is Marine on St. Croix, about one mile south.

A vehicle permit is required for all vehicles entering the park. Day permits cost $7 per vehicle, and an annual permit is $35. Camping reservations can be made through the Minnesota Department of Natural Resources reservation system and are strongly recommended for summer weekends and holidays. The park is open year-round, though some facilities are seasonal. Winter visitors can use the trails for cross-country skiing and snowshoeing when conditions permit.